Math (Calculus 121)
posted by drwls .
The derivative tells you the slope at any point.
df/dx = 8 x^3  12 x
When x = 3, the slope is
m = 8*27  36 = 180
and the equation of the tangent line is
(y  228) = 180*(x  3)
y = 180 x  540 + 228 = 180 x  312
wow, that was absolutely correct (i just plugged it into webassign), thanks a lot!!
please just help me to understand the last part though for the test, where did you get the (y228) = 180*(x3)?
Find the equation of the line that is tangent to the graph of f(x) = 2x4  6x2 + 120 at the point (3, 228).
y=?
The equation for a line with slope m through points x = a and y = b is
(y b)= m (x  a)
That is where the formula came from.
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